Spectrometer

ABSTRACT

A spectrometer includes: a tungsten lamp which emits light with no peak wavelength within a wavelength range of visible light and having a light amount increasing as the wavelength becomes longer; a violet LED which emits light having a peak wavelength within the wavelength range of visible light; a light mixer which mixes light emitted from the tungsten lamp and the violet LED; an etalon which receives light mixed by the light mixer and transmits light contained in the received mixed light and having a particular wavelength; a light receiving unit which receives light transmitted by the etalon; and a measurement control unit which changes the wavelength of light that can pass through the etalon and measures spectral characteristics of the light having passed through the etalon based on the light received by the light receiving unit.

This is a continuation patent application of U.S. application Ser. No.13/227,758 filed Sep. 8, 2011, which claims priority to Japanese PatentApplication No. 2010-262758 filed Nov. 25, 2010 all of which areexpressly incorporated herein by reference in their entireties.

BACKGROUND

1. Technical Field

The present invention relates to a spectrometer which measures spectralcharacteristics of incident light.

2. Related Art

An analyzer which measures light characteristics (such as chromaticityand brightness) of incident light for each wavelength range of the lightis known (for example, see JP-A-2005-106753).

The analyzer disclosed in JP-A-2005-106753 introduces light emitted froma light source and reflected by a sample into a wavelength variableinterference filter, and guides light transmitted through the wavelengthvariable interference filter toward a photo-diode to receive thetransmitted light thereon. Then, the analyzer detects current outputtedfrom the photo-diode to measure the light characteristics. This type ofanalyzer changes light which can pass through the wavelength variableinterference filter through regulation of the wavelength variableinterference filter, thereby sequentially switching from received lightto light having a desired wavelength and allowing the photo-diode toreceive the desired light.

When the light source of the analyzer is constituted by a white lightsource such as a tungsten lamp which does not have its peak wavelengthwithin the wavelength range of visible light, the light amount in theshort wavelength range emitted from the light source decreases. In thiscase, the light amount in the short wavelength range of the entire rangedividable by the wavelength variable interference filter may alsodecrease. Thus, the light amount in the short wavelength range receivedby the photo-diode further decreases, which lowers the measurementaccuracy of the spectral characteristics in the short wavelength rangeand thus makes it difficult to perform accurate measurement of thespectral characteristics of the incident light.

SUMMARY

An advantage of some aspects of the invention is to provide aspectrometer capable of measuring spectral characteristics with highaccuracy.

An aspect of the invention is directed to a spectrometer which divideslight having a wavelength range of visible light including: a firstlight source which emits light with no peak wavelength within thewavelength range of visible light and having a light amount increasingas the wavelength becomes longer; a second light source which emitslight having a peak wavelength within the wavelength range of visiblelight; a light mixer which mixes light emitted from the first lightsource and the second light source; a wavelength variable interferencefilter which receives light mixed by the light mixer and transmits lightcontained in the received mixed light and having a particularwavelength; a light receiving unit which receives light transmitted bythe wavelength variable interference filter; and a measurement controlunit which changes the wavelength of light that can pass through thewavelength variable interference filter and measures spectralcharacteristics of the light having passed through the wavelengthvariable interference filter based on the light received by the lightreceiving unit.

According to this aspect of the invention, the spectrometer includes thefirst light source which emits light without a peak wavelength in thewavelength range of visible light and having a light amount increasingas the wavelength becomes longer, the second light source which emitslight having the peak wavelength within the wavelength range of visiblelight, and the light mixer which mixes light emitted from the respectivelight sources. After the mixture of the light emitted from therespective light sources by using the light mixer, the light receivingunit receives test target light transmitted by the wavelength variableinterference filter, and the measurement control unit measures thespectral characteristics of the test target light. When only the firstlight source which does not have a peak wavelength within the wavelengthrange of visible light is used, the light amount within a specific rangein the wavelength range of visible light considerably decreases asexplained above. According to this aspect of the invention, however, thesecond light source which emits light having the peak wavelengthparticularly in a short wavelength range (wavelength range where thelight amount from the first light source decreases), for example, caneffectively compensate for the light amount in the short wavelengthrange where the light amount from the first light source considerablydrops. Accordingly, the measurement accuracy of the spectralcharacteristics in the wavelength range where the light amount decreasescan improve, which contributes to highly accurate measurement of thespectral characteristics.

It is preferable that the second light source of the spectrometer has apeak wavelength within the range from 385 nm to 450 nm.

When the first light source which emits light having a small lightamount in a short wavelength range such as a tungsten lamp is used underthe condition in which the wavelength variable range of the wavelengthvariable interference filter is set at 380 nm to 780 nm, the lightamount from the first light source decreases particularly in the shortwavelength range. Thus, compensation for the light amount in the shortwavelength range is desired for performing highly accurate spectralcharacteristics measurement. According to this structure, the secondlight source which has the peak wavelength in the range from 385 nm to450 nm is provided to compensate for the light amount in the shortwavelength range. Thus, the light amount in the short wavelength rangesufficiently increases, which raises the accuracy of the spectralcharacteristics measurement.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 illustrates the general structure of a spectrometer according toa first embodiment of the invention.

FIG. 2 is a graph showing spectral distribution of a light source unitaccording to the first embodiment.

FIG. 3 is a cross-sectional view illustrating the general structure ofan etalon according to the first embodiment.

FIG. 4 is a flowchart showing a wavelength correction process executedfor the etalon according to the first embodiment.

FIG. 5 is a graph showing the relationship between current of anelectric signal produced by a light receiving unit and driving voltageaccording to the first embodiment.

FIG. 6 illustrates wavelength correction for the etalon according to thefirst embodiment.

FIG. 7 illustrates the general structure of a spectrometer according toa second embodiment of the invention.

FIG. 8 is a graph showing spectral distribution of a light source unitaccording to the second embodiment.

FIG. 9 illustrates wavelength correction for an etalon according to thesecond embodiment.

FIG. 10 is a graph showing spectral distribution of a light source unitaccording to a modified example of the invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS First Embodiment

A first embodiment according to the invention is hereinafter describedwith reference to the drawings.

1. General Structure of Spectrometer

FIG. 1 illustrates the general structure of a spectrometer 1 accordingto the first embodiment.

As illustrated in FIG. 1, the spectrometer 1 includes a light sourcedevice 2 which emits light toward a test target A, a dividing device 3which has an etalon 5 (e.g., wavelength variable range: 380 nm to 780nm) for dividing test target light reflected by the test target A, and acontrol device 4 which controls the overall operation of thespectrometer 1. The spectrometer 1 is a system which divides test targetlight emitted from the light source device 2 and reflected by the testtarget A by using the dividing device 3, and measures the respectiveamounts of divided light having different wavelengths based on detectionsignals outputted from the dividing device 3.

The spectrometer 1 is also a system which only turns on a violet LED 212(described later) of the light source device 2 to carry out wavelengthcorrection of the etalon 5. In this case, a white standard reflectionplate is used as the test target A. The details of the wavelengthcorrection for the etalon 5 will be described later.

2. Structure of Light Source Device

As illustrated in FIG. 1, the light source device 2 includes a lightsource unit 21, a light mixer 22, and a lens 23 as components combinedinto one body.

The light source unit 21 has a tungsten lamp 211 emitting white light(first light source), the violet LED (light emitting diode) 212 (secondlight source), and a reflector 213 which reflects light emitted from thetungsten lamp 211 and the violet LED 212. The light source device 2turns on both the tungsten lamp 211 and the violet LED 212 at the timeof spectrometry of the test target light, and only turns on the violetLED 212 at the time of wavelength correction of the etalon 5.

The light mixer 22 as a cylindrical or pillar shaped component made ofquartz glass or acrylic resin, for example, mixes the light emitted fromthe tungsten lamp 211 and the violet LED 212, that is, combines thelight reflected by the reflector 213 by multiple reflections within thelight mixer 22.

The lens 23 collimates the light after multiple reflections by the lightmixer 22, and supplies the collimated light toward the test target A.

FIG. 2 is a graph showing the spectral distribution of light produced bythe light source unit 21 according to this embodiment.

The tungsten lamp 211 has the spectral distribution indicated by abroken line in FIG. 2. As can be seen from the figure, the amount oflight emitted from the tungsten lamp 211 increases as the wavelengthbecomes longer. Thus, the light amount is small in the short wavelengthrange around 400 nm.

On the other hand, the violet LED 212 has the spectral distributionindicated by a solid line in FIG. 2. As can be seen from the figure, theviolet LED 212 has a spectral distribution in the wavelength range fromabout 385 nm to about 430 nm, and has a peak wavelength corresponding tothe maximum light amount at the 405 nm wavelength.

In this case, the light emitted from the tungsten lamp 211 and theviolet LED 212 and mixed by the light mixer 22 obtain the spectraldistribution indicated by an alternate long and two short dashes line inFIG. 2. Thus, the violet LED 212 can effectively compensate for thelight amount at the wavelength of 400 nm where the light amount emittedfrom the tungsten lamp 211 decreases (e.g., is low).

3. Dividing Device Structure

As illustrated in FIG. 1, the dividing device 3 includes a device mainbody 30 which has a concave mirror 3A for reflecting the test targetlight reflected by the test target A such that the test target light cantravel in a predetermined direction and converge on the etalon 5. Thedevice main body 30 has the etalon 5 (wavelength variable interferencefilter) which divides test target light received from the concave mirror3A, and a light receiving unit 31 which receives light having respectivewavelengths after division by the etalon 5.

3-1. Light Receiving Unit Structure

The light receiving unit 31 is a light receiving element functioning asa light detector, which is constituted by a photo-diode, a photo-IC orthe like. When receiving test target light transmitted through theetalon 5, the light receiving unit 31 generates an electric signalcorresponding to the amount of the received test target light. Then, thelight receiving unit 31 connected with the control device 4 outputs thegenerated electric signal to the control device 4 as a light receptionsignal.

Generally, a light receiving element has lower sensitivity for lightreception in the short wavelength range than in the long wavelengthrange. In this embodiment, therefore, the violet LED 212 which has apeak wavelength particularly in the short wavelength range as shown inFIG. 2 is employed to improve the sensitivity for light reception in theshort wavelength range.

3-2. Etalon Structure

FIG. 3 is a cross-sectional view illustrating the general structure ofthe etalon 5.

The etalon 5 is a plate-shaped optical component which has asubstantially square shape in plan view, and each side of which is 10 mmlong, for example. As illustrated in FIG. 3, the etalon 5 has a fixedsubstrate 51 and a movable substrate 52. These substrates 51 and 52 arejoined to each other with a junction layer 53 interposed therebetween bya siloxane junction which uses a plasma polymer film or by othermethods, so that the substrates 51 and 52 can be combined into one body.Each of the two substrates 51 and 52 is made of glass such as sodaglass, crystal glass, and quartz glass, or crystal, for example.

A fixed mirror 54 and a movable mirror 55 are provided between the fixedsubstrate 51 and the movable substrate 52. The fixed mirror 54 is fixedto the surface of the fixed substrate 51 opposed to the movablesubstrate 52, while the movable mirror 55 is fixed to the surface of themovable substrate 52 opposed to the fixed substrate 51. The fixed mirror54 and the movable mirror 55 are disposed opposite to each other with agap G left therebetween.

An electrostatic actuator 56 is provided between the fixed substrate 51and the movable substrate 52 for controlling the gap G between the fixedmirror 54 and the movable mirror 55.

The fixed substrate 51 is manufactured from a glass material which is500 μm thick, for example, by etching. As illustrated in FIG. 3, anelectrode forming groove 511 is formed on the fixed substrate 51 byetching so that a first electrode 561 constituting the electrostaticactuator 56 can be disposed within the electrode forming groove 511. Thefirst electrode 561 is connected with the control device 4 (see FIG. 1)via an electrode extension member (not-shown).

The movable substrate 52 is manufactured from a glass material which is200 μm thick, for example, by etching. A second electrode 562constituting the electrostatic actuator 56 is provided on the movablesubstrate 52 in such a position so as to be opposed to the firstelectrode 561 with a predetermined gap left therebetween. The secondelectrode 562 is connected with the control device 4 (see FIG. 1) via anelectrode extension member (not-shown).

According to this structure, the length of the gap G is controlled by anelectrostatic attractive force produced between the first electrode 561and the second electrode 562 in response to voltage outputted from thecontrol device 4, so that the wavelength of light allowed to passthrough the etalon 5 can be determined in accordance with the length ofthe gap G. That is, light which can pass through the etalon 5 isdetermined by the gap length controlled by the function of theelectrostatic actuator 56, so that only the light having passed throughthe etalon 5 can be received by the light receiving unit 31.

4. Control Device Structure

The control device 4 controls the overall operation of the spectrometer1. The control device 4 is constituted by a general-purpose personalcomputer, a mobile information terminal, or a computer used exclusivelyfor colorimetry, for example.

As illustrated in FIG. 1, the control device 4 includes a light sourcecontrol unit 41, a measurement control unit 42, and a correction unit43. The control device 4 further includes a memory unit (not-shown) as arecording medium such as a memory or a hard disk which storestransmission characteristics data (V-λ data) showing wavelengths oftransmission light for driving voltages.

The light source control unit 41 is connected with the light source unit21. The light source control unit 41 outputs a predetermined controlsignal to the light source unit 21 based on a setting input forinitiating a spectral characteristics measuring process received from auser, for example, and allows the tungsten lamp 211 and the violet LED212 of the light source unit 21 to emit light having predeterminedbrightness. Moreover, the light source control unit 41 outputs apredetermined control signal to the light source unit 21 based on asetting input for initiating wavelength correction of the etalon 5received from the user, for example, and allows only the violet LED 212of the light source unit 21 to emit light.

As explained above, the measurement control unit 42 is connected withthe first electrode 561 and the second electrode 562 of the etalon 5.The measurement control unit 42 applies driving voltage to the firstelectrode 561 and the second electrode 562 to vary the length of the gapG of the etalon 5 and switch the wavelength of light which can passthrough the etalon 5.

The measurement control unit 42 is connected with the light receivingunit 31 to perform a process for measuring spectral characteristics oftest target light.

In the spectral characteristics measuring process, the measurementcontrol unit 42 calculates the light reception amount for eachwavelength based on the light reception signal received from the lightreceiving unit 31 to conduct the process for measuring the spectralcharacteristics of the test target light.

The correction unit 43 is connected with the light receiving unit 31 toperform a wavelength correction process for the etalon 5.

In the wavelength correction of the etalon 5, the correction unit 43calculates the relationship between the light reception signal and thedriving voltage based on the reception of the light reception signalinputted from the light receiving unit 31 for each driving voltage.Then, the correction unit 43 calculates the driving voltagecorresponding to 405 nm as the peak wavelength of the violet LED 212 toconduct the wavelength correction of the etalon 5 (correction oftransmission characteristics data mentioned above).

5. Etalon Correction

As noted above, the spectrometer 1 measures spectral characteristics oftest target light having passed through the etalon 5, and also carriesout wavelength correction of the etalon 5 by only turning on the violetLED 212. The wavelength correction of the etalon 5 is herein explainedwith reference to a flowchart shown in FIG. 4.

The coefficient of linear expansion of the etalon 5 which is dependenton the temperatures of the mirrors 54 and 55 and the electrodes 561 and562 varies with the change of the environment temperature. Thus, thesubstrates 51 and 52 may be bent in accordance with the change of theinternal stresses of the mirrors 54 and 55 and the electrodes 561 and562 produced by the change of the environment temperature. In this case,the length of the gap G between the mirrors 54 and 55 varies, whichmakes it difficult to obtain a desired transmission wavelength. It istherefore preferable that the length of the gap G (transmissionwavelength) for each driving voltage is determined beforehand under thecondition of the etalon 5 installed at a predetermined environmenttemperature.

The specific steps of the process are now explained. Initially, thelight source control unit 41 turns on only the violet LED 212 (step S1).The measurement control unit 42 varies driving voltage by 0.1V at atime, for example (step S2). The light receiving unit 31 receives testtarget light reflected by the test target A for each driving voltage,and produces an electric signal corresponding to the amount of thereceived test target light. Based on this signal, the correction unit 43acquires data shown in FIG. 5 which represents the relationship betweenthe current of the electric signal produced by the light receiving unit31 and the voltage (driving voltage) (step S3).

After step S3, the correction unit 43 acquires a voltage V1corresponding to the maximum current based on the data shown in FIG. 5(step S4). The wavelength obtained when the voltage V1 is applied is 405nm (peak wavelength of violet LED 212).

Then, the correction unit 43 reads the V-λ data from the memory unit forcorrection (step S5).

The change pattern of the V-λ data dependent on the environmenttemperature and other factors (such as the change of gravity produced bythe change of the position of the etalon 5) can be simulated beforehand.

FIG. 6 shows a constant wavelength change in accordance with the changeof the environment temperature. More specifically, data beforecorrection is indicated by a broken line, and data after correction isindicated by a solid line in the figure. As can be seen from FIG. 6,correction of only one point of the V-λ data is needed. Thus, thecorrection unit 43 corrects the wavelength corresponding to the drivingvoltage V1 to 405 nm under a predetermined environment temperature.

6. Advantages

According to this embodiment, the spectrometer 1 includes the tungstenlamp 211 which does not have a peak wavelength within the wavelengthrange of visible light, the violet LED 212 which has a peak wavelengthwithin the wavelength range of visible light, and the light mixer 22which mixes light emitted from the respective light sources 211 and 212.After the mixture of the light emitted from the respective light sources211 and 212 by the light mixer 22, the light receiving unit 31 receivestest target light transmitted through the etalon 5, and the measurementcontrol unit 42 measures the spectral characteristics of the test targetlight. When only the tungsten lamp 211 which does not have a peakwavelength within the wavelength range of visible light is used, thelight amount in the short wavelength range of the wavelength range ofvisible light considerably decreases as explained above. According tothis embodiment, however, the violet LED 212 having the peak wavelengthparticularly in the short wavelength range is also provided. In thiscase, the light emitted from the light sources 211 and 212 and mixedwith each other can effectively compensate for the light amount withinthe short wavelength range where the light amount of the tungsten lamp211 considerably drops. Accordingly, the measurement accuracy of thespectral characteristics in the short wavelength range where the lightamount decreases is improved, which contributes to highly accuratemeasurement of the spectral characteristics.

Moreover, the violet LED 212 which has a peak wavelength at 405 nm cancompensate for the light amount in the short wavelength range. Thus, thelight amount in the short wavelength range sufficiently increases, whichraises the accuracy of the spectral characteristics measurement.

Second Embodiment

FIG. 7 illustrates the general structure of a spectrometer 1A in asecond embodiment.

According to the first embodiment, the light source unit 21 includes apair of light sources constituted by the tungsten lamp 211 and theviolet LED 212. In this embodiment, however, a light source unit 21Aincludes a blue LED 214 and a green LED 215 in addition to the lightsources 211 and 212 as four light sources 211, 212, 214, and 215.

FIG. 8 is a graph showing the spectral distribution of light emittedfrom the light source unit 21A in this embodiment.

The blue LED 214 has the spectral distribution indicated by a solid lineL1 in FIG. 8. As shown in the figure, the blue LED 214 has a spectraldistribution within the range from about 420 nm to about 525 nm, and hasa peak wavelength at 470 nm where the light amount becomes maximized.

The green LED 215 has the spectral distribution indicated by a solidline L2 in FIG. 8. As shown in the figure, the green LED 215 has aspectral distribution within the range from about 480 nm to about 610nm, and has a peak wavelength at 530 nm where the light amount becomesmaximized.

The intensities of the peak wavelengths of the violet LED 212, the blueLED 214, and the green LED 215 are designed to decrease as thewavelengths increase.

Therefore, when light emitted from the tungsten lamp 211, the violet LED212, the blue LED 214, and the green LED 215 are mixed by the lightmixer 22, the spectral distribution indicated by an alternate long andtwo short dashes line in FIG. 8 is produced. According to this spectraldistribution, the violet LED 212 compensates for the light amount aroundthe 400 nm wavelength where the light amount emitted from the tungstenlamp 211 is small, and the blue LED 214 and the green LED 215 compensatefor the light amount of the tungsten lamp 211 in the range from theshort wavelength to the long wavelength. Thus, the light amount in thevisible light range increases more than the corresponding amount in thefirst embodiment.

The spectrometer 1A having the light source unit 21A thus constructedperforms wavelength correction of the etalon 5 in the following manner.The wavelength correction of the etalon 5 in this embodiment executedwhen a wavelength change of the etalon 5 is produced by the change ofthe position of the etalon 5 (change of gravity) or the like as well asby the change of the environmental temperature is now explained.

As noted above, the change pattern of the V-λ data can be simulatedbeforehand. When the wavelength change is produced by the change ofgravity or the like as well as by the change of the environmenttemperature, at least three points of the V-λ data need to be correctedas shown in FIG. 9. Thus, the correction unit 43 corrects the wavelengthof the etalon 5 by using the blue LED 214 and the green LED 215 as wellas the violet LED 212.

For the wavelength correction, the specific steps from step S1 to stepS5 shown in FIG. 4 are executed similarly to the first embodiment. Inthis embodiment, however, the steps from step S1 to step S5 shown inFIG. 4 are carried out for each of the blue LED 214 and the green LED215 as well as for the violet LED 212.

By this method, as shown in FIG. 9 the correction unit 43 corrects thewavelength corresponding to the driving voltage V1 included in the databefore correction indicated by a broken line to 405 nm, corrects thewavelength corresponding to a driving voltage V2 included in the databefore correction as the voltage where the current of the blue LED 214becomes maximized to a wavelength λ2 (peak wavelength of blue LED 214),and corrects the wavelength at a driving voltage V3 included in the databefore correction as the voltage where the current of the green LED 215becomes maximized to a wavelength λ3 (peak wavelength of green LED 215)to obtain data after correction indicated by a solid line in the figure.

According to the second embodiment, the following advantages can beoffered as well as the advantages of the first embodiment.

According to this embodiment, the light source unit 21A has the fourlight sources 211, 212, 214, and 215. Thus, the accuracy of thewavelength correction of the etalon 5 in case of a wavelength change canbe raised by using the three light sources 212, 214, and 215 which havepeak wavelengths in the wavelength range of visible light.

Moreover, the respective intensities of the peak wavelengths of theviolet LED 212, the blue LED 214, and the green LED 215 are designed todecrease as the wavelengths increase. Thus, considerable decrease in thelight amount for each wavelength can be avoided by light mixtureachieved by the light mixer 22. Accordingly, the accuracy of thespectral characteristics measurement further improves.

Modifications of Embodiment

The invention is not limited to the embodiments described herein but maybe practiced otherwise without departing from the scope of theinvention. Thus, modifications, improvements and the like including thefollowing changes can be made.

According to the respective embodiments, a second light source isconstituted by the violet LED 212. However, the second light source maybe other light sources as long as they have a peak wavelength within thewavelength range from about 385 nm to about 450 nm. For example, thesecond light source may be an ultraviolet LED whose peak wavelength is385 nm. In this case, the spectral distribution shown in FIG. 10 isproduced as light which can effectively compensate for the light amountaround 400 nm where the light amount emitted from the tungsten lamp 211is small.

According to the respective embodiments, the structure of the etalon 5whose gap G between the mirrors can be controlled by using theelectrostatic actuator 56 has been discussed. However, the gap G may becontrolled by using an electromagnetic actuator having anelectromagnetic coil and a permanent magnet, or a piezoelectric devicecapable of expanding and contracting when voltage is applied thereto,for example.

According to the respective embodiments, the substrates 51 and 52 arejoined to each other via the junction layer 53. However, the junctionsurfaces between the respective substrates 51 and 52 may be joined toeach other by a so-called cold activation junction which activates thejunction surfaces of the substrates 51 and 52, overlaps the activatedjunction surfaces, and pressurizes the overlapped surfaces for junction,for example without forming the junction layer 53. The junction methodfor this purpose may be arbitrarily selected.

According to the respective embodiments, the thickness of the movablesubstrate 52 is set at 200 μm, for example. However, the thickness ofthe movable substrate 52 may be 500 μm equal to the thickness of thefixed substrate 51. In this case, the thickness of a movable portion 521increases to 500 μm as well, which reduces bending of the movable mirror55 and maintains the parallelism of the mirrors 54 and 55 in a morepreferable condition.

While the spectrometer 1 for measuring respective light amounts of lighthaving different wavelengths divided from test target light has beendiscussed in the embodiments, the spectrometer 1 is applicable to acolorimeter which measures chromaticity of test target light, i.e., acolorimeter which analyzes and measures colors of test target A, aspectral camera, or a spectral analyzer.

What is claimed is:
 1. A spectrometer comprising: a first light sourcewhich emits first light with no peak wavelength and having a lightamount increasing as a wavelength of the first light becomes longerwithin a predetermined wavelength range; a second light source whichemits second light having a peak wavelength within the predeterminedwavelength range; a wavelength variable interference filter whichtransmits light having a wavelength varied by a driving voltage; a lightreceiving unit which receives the light transmitted by the wavelengthvariable interference filter; and a correction unit which corrects thedriving voltage based on a relationship between the peak wavelength ofthe second light and the driving voltage when the wavelength variableinterference filter transmits the light having the peak wavelength ofthe second light.
 2. The spectrometer according to claim 1, wherein thepeak wavelength of the second light is within a range of 385 nm to 450nm.
 3. The spectrometer according to claim 1, further comprising: alight mixer which mixes the first light and the second light into mixedlight.
 4. The spectrometer according to claim 1, wherein the first lightsource emits white light.
 5. The spectrometer according to claim 1,wherein the first light source further comprises a tungsten lamp.
 6. Thespectrometer according to claim 1, wherein the second light sourcefurther comprises a violet LED.
 7. The spectrometer according to claim1, wherein the first light source further comprises a tungsten lamp; andthe second light source further comprises a violet LED.
 8. Thespectrometer according to claim 1, further comprising: a third lightsource which emits third light having a wavelength range of about 380 nmto about 780 nm; and a fourth light source which emits fourth lighthaving a wavelength range of about 480 nm to about 610 nm.
 9. Thespectrometer according to claim 7, wherein the third light sourcecomprises a blue LED and the fourth light source comprises a green LED.10. A method for measuring spectral characteristics using a spectrometerhaving a first light source which emits first light with no peakwavelength within a predetermined wavelength range, a second lightsource which emits second light having a peak wavelength within thepredetermined wavelength range, a wavelength variable interferencefilter which transmits alight having a wavelength varied by a drivingvoltage, the method comprising the steps of: (a) turning on the secondlight; (b) measuring spectral characteristics of a white standardreflection plate; (c) correcting a relationship between the peakwavelength of the second light and the driving voltage when thewavelength variable interference filter transmits the light having thepeak wavelength of the second light.